I used math u see when I was in school - from pre algebra through graduation. Now I'm using it with DD - currently in Primer. I feel like the manipulatives are key to this course. It demonstrates how and why math works, not just what to do to get an answer. I love MUS for this reason!

You can usually find manipulatives used - the other day curriculum exchange had a set at a good price. I found mine on Craigslist cheap

It really depends on the child. My oldest could not have done even half as well as she has without the blocks. She is a very hands-on learner. My son, however, has hardly used the blocks at all and he's now in Epsilon (I think -- the fraction book). I'm not sure yet where my youngest will fall.

I recommend getting them. I have three using MUS, and they've all used them for different things at different times. I think they are worth the price; if you decide later you don't need them, you can always sell them.

We bought a set to use this year and I'm glad we did! DD uses them a LOT in Alpha. DS9 doesn't use them almost at all for Delta and DS13 has used them here and there for Epsilon. DS3 thinks they are great fun and I love that he is getting used to them early.